The Hammush is a Hardmodehammer that is purchased from the Truffle for 40 after at least one mechanical boss has been defeated. When swung, the Hammush produces spinning mushrooms like that of the Mushroom Spear, which hurt enemies, even through walls. Like the Pwnhammer (and higher-tier hammers), it can also be used to destroy Altars, and shares its tooltip.
Its best modifier is Legendary. While Light may seem to provide a better speed boost by percentages, rounding reveals that Legendary and Light mine at equal speeds for this tool.
The Hammush's name and design are a reference to the Terraria webcomic "The Legend of Maxx", where Maxx creates a weapon of the exact same name and a design of two Glowing Mushrooms for the hammer head.